Obstructive Shock · What Is It, Causes, Diagnosis, and More…

Obstructive shock refers to the anatomical obstruction of the great vessels of the heart (e.g., superior vena cava, inferior vena cava, and pulmonary vessels) that leads to decreased venous return and/or excessive afterload (i.e., the force that the left ventricle has to overcome to eject blood through the aortic valve), resulting in decreased cardiac output. 

Shock describes circulatory failure and ineffective tissue perfusion that may lead to reversible, or if prolonged, irreversible cellular injury. There are four different types of shock: obstructive, distributive (including anaphylactic, septic, and neurogenic shock), cardiogenic, and hypovolemic shock. Shock is a life-threatening condition and requires immediate medical attention.

Individuals with obstructive shock typically experience respiratory distress and may present with tachycardia, hypotension, tachypnea, air hunger (i.e., an extreme need to breathe), and chest pain. 

A characteristic sign of causative conditions like pneumothorax and tamponade may include dilated and engorged neck veins, resulting from the inability of blood to return to the heart. Various constellations of signs may indicate a probable underlying cause. For example, hyperresonant sounds on percussion, distended neck veins, and absent breath sounds are typically indicative of tension pneumothorax. Distant heart sounds and decreased pulse pressure can usually indicate cardiac tamponade. Tension pneumothorax can mimic the signs of cardiac tamponade, with findings of distended neck veins and hypotension. 

Obstructive shock can be diagnosed based on a thorough review of the individual’s medical history and physical examination. A detailed respiratory and cardiovascular examination is necessary in order to distinguish the underlying cause of obstructive shock. Arterial saturation may also be assessed, using a pulse oximeter, and can be decreased in cases of tension pneumothorax. Lab studies, such as a metabolic panel, lactic acid, arterial blood gas, or electrocardiogram (ECG) are often performed. Imaging studies, such as point of care ultrasound or CT scan, can also assist in assessing the underlying cause. 

Importantly, if an individual is unstable, treatment is typically initiated before imaging has confirmed the diagnosis. The initial treatment for obstructive shock requires resuscitative measures and ABC (airway, breathing, circulation) assessment, which includes supplemental oxygen support and pressure support with intravenous crystalloids. However, fluids should be given with caution, and close monitoring is necessary as excessive administration of intravenous fluids may have a paradoxical worsening of hypotension due to severe right ventricular dilatation, which can affect left ventricular filling. If shock persists despite IV treatment, early initiation of vasopressors (e.g., norepinephrine, or vasopressin) is the first-line choice. The patient may also be intubated if indicated.

Further treatment options depend on the underlying cause of obstructive shock.